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Microsoft Virtual PC Services Insecure Temporary File Creation



Microsoft Virtual PC Services Insecure Temporary File Creation


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                                @stake, Inc.
                              www.atstake.com 

                             Security Advisory

Advisory Name: Virtual PC Services Insecure Temporary File Creation
 Release Date: 02/10/2004
  Application: Connectix Virtual PC 6.0.x
               Microsoft Virtual PC 6.1
     Platform: Mac OS X
     Severity: Local privilege escalation
       Author: George Gal  
Vendor Status: Vendor has updated version of the software
CVE Candidate: CAN-2004-0115
    Reference: www.atstake.com/research/advisories/2004/a021004-1.txt 


Overview: 

Virtual PC is a popular x86 virtual machine emulator capable running
several guest operating systems under the Mac OS X and Windows
platforms. Virtual PC provides a set of services for managing network
sharing capabilities under Mac OS X. These services are spawned from
the setuid root binary, VirtualPC_Services, which creats several
temporary files when it is executed. The VirtualPC_Services does not
check for several unsafe conditions prior to creation of these
temporary files. As a result an attacker with interactive login
access to the system may leverage insecure temporary files to become 
root or overwrite critical system files.


Details: 

@stake has identified a vulnerability within the setuid root binary, 
VirtualPC_Services, due to its inability to check for dangerous
conditions prior to temporary file creation.  This vulnerability
allows an attacker to truncate and overwrite arbitrary files in
addition to creation of arbitrary files with insecure file
permissions.  

Using this vulnerability it is feasible for an attacker to gain root
privileges on the system. The VirtualPC_Services binary creates a
log file upon startup as /tmp/VPCServices_Log.  An attacker may
create a symbolic link in the /tmp/ directory as VPCServices_Log
pointing to an arbitrary file to be overwritten when the
VirtualPC_Services binary is executed. However, when the symbolic
link points to a non-existent file a new file is created with file
permissions determined by the unprivileged user's umask(2) settings.


Vendor Response:

Microsoft has an updated version of the software available.

Download information available at:

http://www.microsoft.com/technet/security/bulletin/MS04-005.asp 


Recommendation: 

If possible install the updated version of Virtual PC.

Do not install Virtual PC on a multi-user machine.  If this is a
requirement, only allow users with in a particular group to access
Virtual PC.


Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned 
the following names to these issues.  These are candidates for 
inclusion in the CVE list (http://cve.mitre.org), which standardizes 
names for security problems.


   CAN-2004-0115

@stake Vulnerability Reporting Policy: 
http://www.atstake.com/research/policy/ 

@stake Advisory Archive:
http://www.atstake.com/research/advisories/ 

PGP Key:
http://www.atstake.com/research/pgp_key.asc 

Copyright 2004 @stake, Inc. All rights reserved.


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